Delivering large doses of drug through the pulmonary route is very difficult. Dry powder inhalers offer advantages in delivering high dose drugs. In a dry powder formulation, choosing a formulation with a high percentage of drug and a low percentage of excipient can help delivery high dose drugs, but it can often be difficult to manufacture and use such powders. Applicants have discovered an ultralow density pulmonary dry powder which allows for high doses of the powder to be packaged in a delivery compartment while being released from the inhaler as highly respirable particles.